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   <title>Using the Concept Hierarchy</title>
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<h2>
<font face="Arial Alternative"><font color="#3333FF">The Jet Concept Hierarchy</font></font></h2>
The Jet system includes a <i>concept hierarchy</i>.&nbsp; This hierarchy
is basically a set of concepts arranged in a tree structure.&nbsp; Associated
with each concept are zero or more words which are instances of that concept.
<h3>
The concept hierarchy file</h3>
The concept hierarchy is defined by a concept hierarchy file.&nbsp; The
file contains lines of the form
<blockquote><font face="Courier New">human
<b>isa</b> thing</font>
<br><font face="Courier New">human <b>words</b> person, man</font></blockquote>
where <font face="Courier New,Courier">human</font> and <font face="Courier New,Courier">thing</font>
are concepts, and <font face="Courier New">person</font> and <font face="Courier New">man</font>
are words;&nbsp; <b><font face="Courier New">isa</font></b> and <b><font face="Courier New">words</font></b>
are the only two keywords. This file indicates that <font face="Courier New,Courier">human</font>
is a subtype of <font face="Courier New,Courier">thing</font>, and <font face="Courier New,Courier">human</font>
is associated with the words <font face="Courier New">person</font> and
<font face="Courier New">man</font>.
Concept names should begin with a lower-case letter, and may contain lower
and upper case letters;&nbsp; a word is normally all lower case. No two
concepts in the hierarchy can have the same name, and no two words in the
hierarchy can be the same. A concept name and a word can be the same though.
<p>Concept hierarchy files should typically have the file extension&nbsp;
<tt>.hrc</tt>.
<h3>
Loading the concepts</h3>
A concept file can be loaded into the system by including a line of the
form
<blockquote><tt>Concepts.fileName</tt> = <i>filename</i></blockquote>
in the Jet properties file.
<h3>
Using the concepts</h3>
In an annotation pattern element, in place of a feature test of the form&nbsp;&nbsp;
<tt>feature=value</tt>&nbsp;&nbsp;&nbsp; , one can have a test of the form
<blockquote><tt>feature ?isa(</tt><i>concept</i><tt>)</tt></blockquote>
This feature test succeeds if the value of feature is a word associated
with <i>concept</i>, or associated with some <i>concept</i>' which is a
descendant of <i>concept</i> in the hierarchy.
<h3>
Using the Concept Hierarchy UI</h3>

<p><br>The Concept Hierarchy UI is an editor for concept hierarchy (.hrc)
files. You start the Concept Hierarchy UI by selecting "Concept Window"
in the Jet File menu. If a hierarchy has been specified in the Jet properties
file, it will appear
<p>The Concept Hierarchy UI has the basic features of an editor such as
those for a text editor.
<p>File Open, Save, SaveAs and Exit do the standard file IO (note that
Exit quits Jet, not just the UI). If a concept hierarchy file is changed
after it was last saved, it is marked as dirty with an asterisk after the
file name in the window caption. A dialog message will pop up asking if
the current file is to be saved. There is a bug here: if the window is
being closed when the file is dirty, a dialog pops up, and then the "cancel"
button is pressed, the window will become invisible without anything done
to the file. If the "Exit" menu item is chosen instead, everything works
just as fine.
<p>From the "Edit" menu, you can add, delete, rename and search concepts
and words. There is a bug here: when you rename a concept or word either
by selecting the "Rename" menu item or clicking on the concept or word
itself, then type in the new name and carriage return, an error message
will pop out if the new name is an empty string or causes duplicate in
the hierarchy. After you press OK to get rid of the message, the concept
or word is still being edited, if you press ESC, the bad name will be accepted.
It's the user's responsibility not to deliberately introduce this kind
of error into the file at the time being because the editor is not so stubborn
as to give the same advice twice.
<p>The Drag-and-Drop feature has been added to the editor, making it easier
to move a large portion of a hierarchy from one place to another. Note
that only move is provided but not copy, even though by pressing CTRL when
dragging a node, the cursor will have a "+" sign. The copy function is
not provided because no duplicate concepts and words are allowed in a hierarchy.
<br>&nbsp;
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